The most serious adverse response associated with the use of contact lenses is corneal ulceration. The risk of development of such ulcers is particularly associated with the use of soft lenses in an extended wear mode, that is, when the lens is worn continuously, without removal during sleep. Such ulcers can lead to perforation of the cornea, or can leave corneal scars which cause permanent partial vision loss. The most threatening ulcers are those caused by microbial agents such as Acanthamoeba or bacteria such as Staphylococcus epidermidis, Staphylococcus aureus, Streptococcus pneumoniae and Pseudomonas aeruginosa.
The healthy eye uses a number of mechanisms to defend itself from infection by pathogenic bacteria. Lysozyme, one of the principal proteins found in tears, is known to kill common Gram positive bacteria by hydrolyzing and dissolving parts of their exterior membranes. Other proteinaceous tear components such as complement proteins and immunoglobulins such as secretory IgA contribute to this defense system. Lactoferrin is a tear protein which is bacteriostatic by virtue of its ability to bind iron and thus make it unavailable to bacteria. Bacteria cannot maintain sustained growth in the absence of iron. Also, other trace metallic elements such as calcium, copper, magnesium, molybdenum, and zinc are essential co-factors for many bacterial enzymes such as proteinases. In many cases, it is the action of such enzymes on tissue of the eye that causes much of the damage during a bacterial infection of the eye.
This invention is based upon the discovery that soft contact lenses can be prepared from polymers that contain metal chelating functionality, and that such lenses have the ability to chelate metals such as iron, calcium, copper, magnesium, molybdenum, and zinc, and thus make such metals unavailable to bacteria.